I moved my Ryzen 7 5700X system to a Gigabyte B550 motherboard, and now the CPU temperature jumps to around 100°C almost immediately after entering BIOS, triggering a thermal shutdown. The radiator fans are quiet at first and then ramp to full speed. The NZXT Kraken's SATA power is connected directly to the PSU, while its pump connector is attached to CPU_FAN. I removed the block to check for protective film and mounting problems; the paste pattern looked normal and no film was present. Both tubes feel cold, although there is a slight vibration suggesting the pump motor is trying to run. After shutdown, the pump block is extremely hot while the tubes remain cold, which suggests the heat is reaching the block but coolant is not circulating. Could this be trapped air, an internal blockage caused by moving the radiator, or a failed impeller? Is there a safe way to clear it before replacing the cooler with an air cooler?
3 Answers
This is also a good example of why an air cooler is useful for troubleshooting. If the system runs normally with the air cooler, the CPU, socket, and motherboard are almost certainly fine and the AIO is the failed part. Do not keep rebooting into BIOS with the faulty cooler; repeated thermal shutdowns are unnecessary, even though the processor has built-in protection.
The temperature difference is the key clue. A hot block with cold tubes usually means the block is making proper contact with the CPU, but coolant is not leaving the pump chamber. That points much more toward a failed impeller, seized pump, or internal blockage than a mounting issue. Slight vibration only proves the motor is attempting to operate; it does not prove that the impeller is moving fluid. If the pump RPM reading is available in firmware, check it, but a replacement cooler or an RMA is probably the practical fix.
You can try powering the system off, gently rotating or tilting the case through different orientations, and then testing it briefly, but do not shake the cooler aggressively or keep running it while the CPU is overheating. Air can sometimes move away from the pump, but it will not revive a seized impeller or clear a real internal blockage. Since the issue appeared after moving the build, inspect the pump connector and SATA power connection once more, then use a cheap air cooler to confirm the CPU and motherboard are fine.
I will avoid running it for long and use a temporary air cooler if needed. The power connections are secure, so I am leaning toward replacing or warranty-servicing the AIO.
I checked the block immediately after shutdown and it was very hot, while both tubes stayed cold. I cannot reach the pump-RPM screen before the system shuts down, so a failed impeller or blockage seems likely.